Pilot study to examine the effects of intravenous immunoglobulin (IVIG) in children with autism. The hypothesis to be tested is that treatment of children with high dose IVIG (2mg/kg) will result in improvement in autistic characteristics as measured with standardized behavioral ratings. Recent research has shown a number of immunological abnormalities in individuals with autism. A small study by Gupta, et al, 1996, administered IVIG in replacement doses to 10 autistic children and reported improvements in autistic characteristics. No standardized outcome measures were used in this study. The investigators propose to use immune modulating doses of IVIG in combination with standardized diagnostic instruments and behavioral rating scales to provide information about the possible efficacy of high dose IVIG in children with autism. The study will provide information about the feasibility of performing a larger, double-blind, placebo-controlled study to determine whether IVIG is a viable therapeutic option for children with autism. Specific Aims: 1) Assess the efficacy of IVIG treatment in improving autistic characteristics including speech and behavior 2) Evaluate the lymphocyte phenotype, and autoimmune activation markers in patients with autism before and after treatment with IVIG 3) Correlate changes in immunologic and clinical parameters after treatment with IVIG